Split the `docs` service out of `local.yml`

[browniebroke]

Description

Related to #4865: by default, the docs service is tarting by default with the app when running docker compose -f local.yml up. I find this to be a surprising behaviour. When running that command, I want to start the app, not the docs.

I'm suggesting to split out the docs service into its own docker compose config docs.yml, which could be combined with the main local.yml, if needed: docker compose -f local.yml -f docs.yml up docs.

Rationale

Be more intentional about which services are being started.

The main inconvenient I can see is that the command to run the docs is a bit longer, but that could be solved with alias or makefile.